LOCOMOTOR SYSTEM 643 



The calculation of the daily work performed by horses, either in 

 saddle or draught, can only be roughly approximate. The following 

 formula gives the result in foot-tons for saddle-horses : 



{W+W^xD , 

 Fx 2240 ' 



where W is the weight of the horse ; 



W 1 the weight carried in pounds ; 

 D the distance travelled in feet ; 

 F the co-efficient of resistance ; 

 2240 the number of pounds in a ton. 



For the purpose of ascertaining the energy expended in draught, 

 it is necessary to know the force of traction. This is a variable 

 quantity depending on the load and the nature of the road ; but 

 the dynamometer gives it with sufficient approximation. The 

 formula then becomes — 



( W+ W)xD TxD 

 Fx 2240 2240 ' 



The first part of the formula remains as before, in the second half — 



T=the force of traction in pounds. 

 Z) = the distance travelled in feet. 

 2240 = the number of pounds in a ton. 



As a guide to the force of traction, the following results have been 

 obtained by experiments with vehicles on a level road : 



lbs. 



It must not be forgotten that in addition to the effort required 

 to carry or drag a load, there is another source of expenditure — i.e., 

 the force required to move the animal's own body. Many observa- 

 tions have been made by Zuntz and Lehmann to ascertain what this 

 amounts to on the basis of the oxygen absorbed. For a horse 

 weighing 500 kilogrammes (1,100 pounds) they found that the effort 

 necessary to move the body was equal to 22*4 kilogrammeters 

 of work for every meter (3 feet 3 inches) travelled.* That is 

 to say, the resistance the body offers to being moved is over- 

 come by a force of 50 pounds for every foot of ground passed 

 over. Fifty pounds are ^2 of the animal's body weight. This 

 number is known as the co-efficient of resistance. The value of the 

 co-efficient depends upon the pace — the higher the velocity, the 

 greater the resistance — and, in consequence, a greater effort is 

 required to transport the body. In man the co-efficient of resist- 

 ance at three miles an hour is , at four miles an hour — ^ — , from 



20-59' 16-74' 



which it would appear that the horse moves his body weight with less 

 effort than does a man. The co-efficients for the higher velocities 



* Experimental Station Record, Agricultural Department, U.S.A., vol. vii., 

 No. 7, 1895. 



